In an increasingly mobile world, consumers have quickly embraced wireless technologies such as WiFi and Bluetooth to make their workspace less cluttered and more convenient. In order to power an ever growing assortment of battery operated devices, a consumer must deal with a large collection of bulky transformers and an unsightly, frustrating wire nest. Mobile users and travelers are often forced to lug a tangle of chargers and they often suffer for leaving one behind. In front of a cheering audience at the All Things Digital conference on Jun. 1, 2006, Martha Stewart brought a jumbled mess of power adapters to the microphone and challenged the tech community to find a solution [22].
There have been several attempts to bring a wireless power solution to consumers. The most common wireless systems charge our electric toothbrushes and razors. Two newer technologies, by SplashPower and Dr. Ron Hui of City University of Hong Kong, have also been presented.
Many electric toothbrushes and razors employ a voltage reducing transformer with no metallic contact between the primary and secondary side. For the efficiency of power transfer, designers typically incorporate ferromagnetic cores that provide a low reluctance path for magnetic fields traveling from the primary 100 to the secondary 110 windings, as illustrated in FIGS. 2A, 2B, and 2C. However, devices typically need to be placed in a very specific position or orientation with respect to the base station to be charged efficiently, or to be charged at all. In addition, the physical dimensions, such as the depth and weight of the components, can often make this system unsuitable for today's lightweight portable electronic devices.
SplashPower, founded by two Cambridge University students in June 2001, has disclosed a system that uses two perpendicular coils to create an even magnetic field distribution over a planar surface, as shown in FIG. 3. The coils alternate switching on and off to create two perpendicular magnetic fields, parallel to the base stations surface. When a device with a secondary winding having a highly permeable core is placed on the base station, magnetic fields will tend to travel through the low reluctance core rather than the surrounding air as shown in FIG. 4. FIG. 4 shows cross sectional views of SplashPower base station illustrating magnetic field lines (1), where the top figure shows undisturbed (no device present) field lines during normal operation and the middle figure shows the effect of placing a piece of ferromagnetic material (800) in the magnetic fields. The field lines can be seen traveling through the core rather than the surrounding air. The bottom figure simulates two individual cores in the magnetic field. Again, the magnetic fields travel through the core material rather than surrounding air. SplashPower indicates that specially equipped electronic devices can receive charge in any position or orientation on top of the base station. The SplashPower design has receivers built to include a dense ferromagnetic core, which would add undesirable bulk to small devices. As the SplashPower base station uses a two coil layout, it may waste large amounts of power, especially if a user attempts to charge a device in the corner of the pad. SplashPower's base station can be thick and clunky due to the inclusion of a dense ferromagnetic core.
Dr. Ron Hui, Chair Professor of Hong Kong City University's Department of Electronic Engineering, has disclosed a wireless power system having a transmitter claimed to create an even magnetomotive force in the immediate vicinity, by using a three layer array of hexagonal inductive coils, as shown in FIG. 5. FIG. 6 shows an mmf scan of a single layer, while FIG. 7 shows an mmf scan of the three layers. The inductive coils are coreless to allow a small, lightweight, low cost system. A receiving coil placed on top of the transmitter as shown in FIG. 5 can be used to charge an electronic device. However, interactions between multiple layers may hinder system performance, and the fabrication of multilayer PCB boards is considerably more expensive than single layer boards.
There is a need for a method and apparatus to reduce, or even eliminate, the need for a myriad of power supplies and wires in an efficient mariner.